Are mosquitoes a secret killer whale killer?

Not the wild orcas in the Gulf of Mexico, of course, but rather captive orcas at places like Sea World, in San Antonio.

Orcas at San Antonio. (Sea World)

It turns out that captive orcas behave differently than their wild counterparts: they spend hours during each day, mostly at night, floating motionless, a behavior known as logging.

And there’s another important distinction. As mosquitoes can only lay their eggs in still water, there are no bloodsuckers out to sea. But alas that’s not the case on land.

A new report (see article) in the Journal of Marine Animals and Their Ecology finds that orcas are especially vulnerable to mosquitoes while logging.

“Mosquitoes are attracted to exhaled carbon dioxide, heat and dark surfaces, all of which are present during logging behavior,” the authors state. “Further, captive orcas are often housed in geographic locations receiving high ultraviolet radiation, which acts as an immunosuppressant. Unfortunately, many of these facilities offer the animals little shade.”

The authors note two reports of captive orca deaths due to mosquito-borne illnesses: St. Louis Encephalitis Virus was implicated in the 1990 death of the male orca Kanduke, at SeaWorld of Florida, and West Nile Virus killed the male orca Taku at SeaWorld of Texas in 2007.

The official cause of Taku’s death was “pneumonia” without any reference to a mosquito bite, but a subsequent analysis of the whale’s death showed it was indeed West Nile Virus that caused its death.

To combat this problem, at a minimum, facilities housing orcas should provide adequate shade structure, strive to control mosquito breeding habitat, and improve surveillance of mosquito species, the authors say.